Febrile Seizures: What Could Cause Them?

Febrile seizures are seizures that are observed in small children and infants. They are associated with a fever, but without the presence of an intracranial infection or other defined cause. These seizures usually coincide with a loss of consciousness and can last from 15 seconds to almost 15 minutes. Febrile seizures are relatively common (1 in 25 children will have at least one of these seizures) and can be frightening to watch; however, most febrile seizures are short and harmless. The risk factors for developing febrile seizures are young age during the first seizure, a family history of such seizures and frequent fevers.

What research is being done to find the cause?
Experiments in animal rodents reveal that hyperthermia (increase in body temperature) can lead to hyperventilation, which eventually leads to blood alkalosis (excessively basic), hypocapnia (reduction in blood CO2 levels) and seizures. The researchers in a recent study wanted to see if this was the case in humans as well. The subjects were children with febrile seizures; controls were children with fever but without seizures. Blood was collected from the children and blood pH (a measure of acidity or alkalinity) and blood pCO2 (partial pressure of carbon dioxide, a measure of the amount of CO2 released into the blood) were measured.

These were the results:

There were no differences in blood pH between children that had febrile seizures and those that had fever without seizures.

When observed one hour after seizure, children with febrile seizures had lower blood pCO2 as compared to controls.

This reduction in pCO2 was more pronounced in children with complex febrile seizures (defined here as seizures lasting longer than 15 minutes or those that recur within 24 hr) as compared to children with simple febrile seizures (seizures shorter than 15 min).

Why is this study important?
This study is one of the few to investigate the relationship between hyperthermia and hypocapnia in human subjects. A small percentage of children that have had febrile seizures do go on to develop temporal lobe epilepsy later in life; finding out whether hypocapnia is a contributing factor could be a worthwhile study.

Although the results are intriguing, the study needs to be replicated with a larger sample size. In addition, the correlation between hyperthermia and hypocapnia does not necessarily mean that hypocapnia is what causes seizures or epilepsy in the long term.